It is previously known a variety of lock devices that use electronic devices for increasing the security of the lock and for providing effective administration, management, and control of keys and personnel. However, the demand for lock systems with a high level of security and at the same time being easy to administer is constantly increasing.
The UK patent application GB 2 309 046 discloses a lock that sends a random number to a key, which applies a crypto algorithm to the random number and sends a code word back to the lock. In the lock, the code word is compared with a desired code word, which is generated by applying the same crypto algorithm to the random number. An authentication signal is then generated so long as the code word and the desired code word are substantially but not necessarily completely in agreement. The described key and lock system has several limitations and drawbacks. The communication between lock and key is wireless, introducing noise in the transmitted information. Therefore, the level of security is decreased as a certain degree of mismatch between the results calculated in the lock and the key must be allowed. This might be allowed in a car lock application, as is the case here, but not in normal lock applications. Furthermore, the key is limited to the use with one single lock, thus making the system unusable in a master key system.
The European patent application EP 0 816 600 discloses a single key system comprising a lock, keys and a codifier. The lock includes an electronic circuit which stores an access code and identification codes for the keys with specific restrictions. The keys include electronic circuits that store the access codes for one or several keys. However, one drawback with the described single key system is that it is possible to read out or intercept data, lowering the level of security.